Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Master of Science (MS)

Department / School

Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) have already improved their power conversion efficiency (PCE) from 3.9% to ~22.1% at present. This demonstrated that PSCs can be a promising alternative to conventional silicon solar cells. PSCs have been marked as one of the most favorable next-generation solar cells due to their high extinction coefficient, broad light absorption range and ambipolar charge transport properties, low production cost, and simple fabrication processing. Various device architectures have been designed and investigated for constructing high performance PSCs consisting of different electron transport layers (ETL) and hole transport layers (HTL). In general, PSCs are fabricated in two structures: mesoporous scaffold n-i-p and planar heterojunction p-i-n PSCs. Although mesoscopic PSCs have obtained an impressive PCE, it requires high temperature process (> 450oC) for forming compact TiO2 and mesoporous TiO2 that hinders their applications that require mechanical flexibility. On the other hand, planar p-i-n PSCs have drawn attention due to low temperature processing, mechanical flexible devices. The goal of this work is to introduce a non-conjugated polymer material Polyvinylpyrrolidone (PVP) as cathode buffer layer (CBL) and understand interfacial engineering in planar p-i-n PSCs. PVP was used for the first time as a CBL in PSCs. The ETL and HTL are highly responsible to increase carrier separation, improve charge collection and reduce recombination. Additionally, the buffer layer between ETL and metal cathode (like Ca, Al, Ag) electrode in PSCs plays a crucial role in energy-level alignment, trap state passivation and PSCs film morphology. A comparative study on PSCs without and with CBL was investigated where rhodamine as CBL was considered for control device. The thickness of PVP CBL was analyzed by changing spin speed from 1000 rpm to 5000 rpm at an interval of 2000 rpm. The optimal spin speed was found at 3000 rpm, which achieved an average efficiency of 15.30%. The concentrations of PVP dissolved in isopropanol was optimized from 0.5 mg/ml to 2.0 mg/ml. There was simultaneous enhancement of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and overall power conversion efficiency (PCE) due to incorporation of PVP. The best device achieved a PCE of 16.35%. Various device characterizations such as atomic force microscopy (AFM), scanning electron microscopy (SEM) etc. were performed to interpret the enhancement of device performance.

Library of Congress Subject Headings

Perovskite.
Solar cells -- Materials.
Photovoltaic cells -- Materials.

Description

Includes bibliographical references (68-72)

Format

application/pdf

Number of Pages

83

Publisher

South Dakota State University

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Rights Statement

In Copyright